Thursday, September 27, 2018

Colpitts Oscillator


Colpitts Oscillator






Transistor 2N3904 CBE (C to g31 / B to g32 / E to g33)

C1 = 1uF (Negative stripe goes to negative voltage – other leg goes to j31)
C2 = 33nF (g27-g29)
C3 = 10nF (h29 – h31)
C4 = 47nF (d29 – d31)
C5 = 100nF (h37 – h39)

R1 = 15k (h32 – positive voltage)
R2 = 5.6k (i32 – negative voltage)
R3 = 68 (g36 – negative voltage on other side)

Jumper wires:
e29 – f29
j27 – positive voltage
Negative voltage – other negative voltage
j31 – j37
h33 – h36
c31 – f33

Oscilloscope probe = g39 and ground clip attached to inductor L1’s i27 leg





Shorter jumpers are better because breadboards have parasitic inductance that adds to the inductor’s parameters. I had a few really long jumper wires-when I shortened them the circuit worked.

I think C1 (the electrolytic capacitor) shorts the “Base” (B) of the transistor so that you get an output AC wave. Oscillation = waves = alternating = AC. I forgot to put my oscilloscope on ‘AC’ setting so I was getting weird displays.

This circuit was much harder to get going than anything I’ve put together. Even when my Chua chaotic circuits are misbehaving I still see something sort of cool. This thing is all or nothing.

I have some variable capacitors I’m going to plunk in and play with to see what slight adjustments do to the waveform and frequency.